1. Preheat oven to 250 degrees Fahrenheit.
2. Beat egg whites until stiff; set aside. Beat yolks 10 minutes; add oil, vanilla, lemon juice, then sugar. Gradually add potato starch while mixing. Gently fold yolk mixture into whites.
3. Pour batter into an ungreased tube pan. Bake at 250 degrees for 10 minutes; raise oven temperature to 300 degrees for half an hour, 325 degrees for 15 minutes, then 350 degrees for 25 minutes.
4. Remove from oven and immediately invert over a soda or wine bottle and allow to cool completely.